ASoC: rt5670: Add disabled item in dmic pin enum

Currently, we will configure dmic related pin definition if pdata.dmic_en
is true. However, there is no disable option in the enum. So, any dmic is
used, all 3 dmic related pins will be configured. It may cause unexpected
pin definition. This patch adds a disable item for each dmic enum and
take it as default. So the driver will not set the pin configuration if
we don't set dmicx_data_pin in platform data.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>